Link to post

Share on other sites

if you simplify your thinking, you might realize that the addition of what you call slip is merely the thickening of part of the wall of the pot. nothing sacred, special or scary about it, you are just adding some more clay that happens to be very wet. putting it into a pleasing shape will simply add a pleasing shape to the pot. whatever covering you choose later is the same as covering the original pot, just a little thicker some places.

Share this post

Link to post

Share on other sites

Just tried this with two 50 ml samples of Alberta Slip. Added 1 tbsp of vinegar to one & 1 tbsp of sodium silicate to the other. That's a lot for just 50 ml samples but I wanted to see what would happen. The vinegar worked better to thicken up this slip. There must be a lot of calcium carbonate in Alberta Slip - it really fizzed, then thickened up nicely. I'll leave the samples to sit around for awhile to see if sodium silicate just takes more time to work.

Share this post

Link to post

Share on other sites

Guest

Guest

I had made some slip from the clay I was using to try slip trailing. When it started to get smelly I added some vinegar. A couple of days later I went to check to see if it still smelled bad and noticed the slip was thicker.

And here I thought I discovered something new...

Share this post

Link to post

Share on other sites

The result you got with the vinegar and sodium silicate is exactly what should be expected. The vinegar is a flocculant and will cause the glaze or slip to appear thicker, with a higher viscosity. The sodium silicate is a deflocculant and will cause the opposite, the glaze or slip will appear thinner, with a lower viscosity. However, the issue with slip is not that you are seeking a lower or higher viscosity, but that you are seeking a higher specific gravity. What you want with a trailing slip is not simply thicker slip, but more clay particles in the same volume of slip. Thus, the slip will not shrink as much when it dries. To achieve this, one must first deflocculate the slip, causing it to become thinner and almost too watery, and then add more dry clay to thicken it. If you try to just add more clay until you can't mix it anymore, you still won't have enough clay in the slip. Deflocculate it, and bingo, you now can put in a lot more dry clay and it will still flow (but not shrink as it dries).

Share this post

Link to post

Share on other sites

edit: The only other thing is I would add is sieving it before using. I use a 60 mesh and instead of brushing it through I thump the sieve (with a batt on top as a lid) so it falls through the sieve, less air bubbles that way.

It's hard to describe but if you overdo it with the flocs and deflocs going back and forth it can get so it kinda does a sagging slumpy thing down vertical walls on a pot and doesn't hold it's form as well.

Share this post

Link to post

Share on other sites

Sodium silicate is also called water glass, was sometimes used to pickle eggs. However, you probably won't find it in a modern grocery. But because it's usage is common among potters, you should be able to find it at your preferred local pottery supplier. Same for the Darvan. Or consult the usual online suspects selling pottery materials.

Share this post

Link to post

Share on other sites

Guest

Guest

Thanks Dick, the closest pottery supply place is a 2 hr drive each way (4 hour round trip). I plan on putting an order together and have it UPS'd to me once I need some other stuff. But in the meanwhile...

Sodium silicate is also used as a cement floor sealer, I can buy a 5 gallon bucket of the stuff locally. I just need to figure out what to do with the other 4-3/4 gallons I think the price is around $220.

Sodium silicate is also used to repair radiators and gaskets. Bar's Leaks Stop Leak orHead Gasket Repair might fit the bill but I think there's some type of fibers that might need to be strained out and there might be some copper in there as well.

Share this post

Link to post

Share on other sites

You can get the sodium silicate through Amazon and some other online sources, but the shipping costs are high (higher than I think they should be, but that's a different issue). The issue with sodium silicate in large quantities is that it does not keep well, it goes jelly and then hard. So a small pint or so is all I'd get, unless you are going to be doing a lot of slip casting and need it by the barrel. Darvan keeps better, but seems to be purely a pottery material. You'd have to order it from one of the pottery suppliers, and again you fight the shipping cost battle. For right now, you could achieve what you need to with some saturated soda ash solution. Fill a small jar with hot water and add the dry soda ash a bit at a time. Cap the jar and shake it until the soda ash has dissolved. Then add some more, rinse and repeat. Keep adding the soda ash until finally no more will dissolve when you shake it. There will be a few crystals remaining on the bottom of the jar that just won't go away. Now the solution is saturated with as much soda ash as it will support. Splash some of this into your gloppy slip mix and watch it go liquid. Then add more of your dried clay until it is too thick to stir. Finally add another splash of the soda ash solution to defloc the additional clay you just added.